In some service provider networks, it may be advantageous to use aggregating packet switches with moderate or low sophistication to aggregate packets received from subscriber networks onto one or more trunk links that are connected to a more sophisticated packet switch.
In some cases, a subscriber may want two or more of its locations to be able to communicate with each other. The service provider may enable communication between the subscriber locations, but may want to monitor the communication. For example, the service provider may want to measure the amount of data exchanged by the subscriber locations so that the service provider may provide usage-based billing for the communication.
To enable such communication, the service provider network may connect the two or more subscriber locations together using a layer-two mechanism such as a Virtual Local Area Network (VLAN). However, if a VLAN is used, communication between the subscriber locations may take place in an aggregating packet switch rather than in the more sophisticated packet switch.
Unfortunately, the aggregating packet switch may lack the sophistication needed for monitoring usage and may thus prevent the service provider from offering usage-based billing. To overcome this limitation, the service provider may, at great expense, deploy more sophisticated packet switches that are capable of providing the monitoring necessary for usage-based billing in place of the aggregating packet switches.
Alternatively, the service provider may force communication between the subscriber locations to take place in the more sophisticated packet switch to which the aggregating packet switch is connected. To preclude communication in the aggregating packet switch, the service provider may assign each subscriber location to a different VLAN and then use layer-three routing functionality in the more sophisticated packet switch to route packets between the different VLANs. This approach may be undesirable since it requires the use of layer-three techniques that are expensive in terms of both capital expense and operating expense.